The present invention relates to spark plugs for internal combustion engines, and more particularly the invention relates to an improved spark plug which is highly resistant to carbon fouling.
It has been the tendency of the previously known spark plugs to cause incomplete combustion due to the flame propagation, thus causing a carbon deposition on the surface of the insulator leg portion and thereby causing insulation failure and misfiring. This has also been confirmed from the fact that carbon fouling increases as the spark timing is advanced even if the other conditions are maintained the same.